Aluminum base alloys



Patented Feb. 5, 1952 ALUMINUM BASE ALLOYS Charles B. Willmore, North Aurora, 111., assignor to William F. Jobbins, Incorporated, Aurora, 111., a corporation of Illinois No Drawing. Application May '10, 1949, Serial No. 92,500

4 Claims.

1 This invention relates to aluminum base alloys and particularly to casting alloys of the type constituted with copper, silicon and zinc as major alloying elements with aluminum.

Alloys of this type consist essentially of aluminum with 2 to 4 percent copper, 2 to 8 percent silicon, and 2 to 8 percent zinc. Compositions formulated of these primary metals have not enjoyed extensive commercial use because they suf-.

fer from undesirable casting characteristics and sand or chill casting and they may be evident in castings which have been subjected to heat treatment with or without subsequent artificial ageing.

Another object is to provide for improved physical properties, and improved castability in an aluminum base alloy containing silicon, copper, and zinc as major alloying elements.

A further object is to produce a new and improved casting alloy based on the system, aluminum, silicon, copper, zinc and magnesium with other minor alloying elements, notwithstanding the presence of limited amounts of impurities, such as iron and nickel.

The objects of this invention are achieved by the addition of certain metallic components to a basic composition of aluminum, copper, silicon, and zinc, to provide an alloy having more desirable casting characteristics and improved 'physical properties. The new and improved composition is adapted for use interchangeably or tselectively in sand or similar slow cooling molds, or it may be chill cast in permanent molds of metal,

graphite, or other relatively rapid cooling material. They may be used in as cast condition or their physical properties may be desirably altered by heat treatment, such as solution heatitreatment and quenching, with the possibility of securing still further improvement by following heat treatment and quenching steps with artificial ageing. This hastens the reprecipitation of components such as CuAlz, which had been dissolved during solution heat reatment to form a supersaturated solution, a f

A particular casting characteristic which is markedly improved by the practice of this invention is often referred to in the trade by the term shrinkage. As used herein, the term is not applied to proportional change in all dimensions that results from the natural contraction of the metal volumeas it passes from molten to solid state. It is used to refer to the undesirable phenomenon, of a local character, resulting in actual defects in the ultimate product which may appear either as porous internal holes in the casting, or as depressions or porous regions at the surface.

By way .of explanation, it will be understood that as the metal passes from the liquid to the solid state, the change does not occur immediately and simultaneously throughout the mass. Instead, numerous small isolated crystalline nuclei form, and as freezing progresses each nucleus grows to form branches or dendrites. As neighboring dendrites-meet and cannot grow any further, the meeting lines form inflexible grain boundaries. The conversion of liquid metal to solid form causes a natural decrease in volume with a result that the metal remaining within the dendrites is insufiicient to satisfy the volume requirements defined by the grain boundaries. Thus, as finally complete solidification is approached, there is a tendency toward the formation of voids or spaces between the dendrites and at the rain boundaries. Such spaces constitute low pressure areas which tend to become filled by at least one of various means.

If there is sufficient liquid metal still available and if channels remain open between the dendrites to make the voids accessible, then sufficient liquid will flow in to the ,voids to produce complete soundness in the solidified structure. If the amount of liquid remaining is insufiicient or if they are blocked from the voids, then the spaces remain as open low pressure areas, or the pressure may be released by gases which have been dissolved in the metal and come out during freezing. In either event, the latter conditions result in microporosity which constitutes a defect of an undesirable character in the final product.

In the absence of gas or, in the absenc of accessible liquid metal to the microscopic spaces, the low pressure that is developed may be relaxed by collapse of the entire structure, causing a depression at the surface of the casting. The collapse may be of a local internal character, which causes the microporosity to collect into a lesser number of larger voids to form pin holes orpipes of an undesirable character.

It is possible to overcome these defects, hereinafter combined under the term high shrinkage," by the employment of precautions in mold design, such as by the proper placement of gates and risers to provide reservoirs of liquid metal for feeding to the shrinkage areas, and the provision for selective chilling to initiate solidification at selected areas so that freezing will proceed progressively toward the risers. However, the employment of these precautions in foundry practice adds greatly to the expense of the molding and casting operations.

Methods for determining shrinkage tendency in casting alloys are usually incapable of standardization and determinations are made on a comparative system employing as the testing medium a standard mold which is difficult to cast. The method employed to test the compositions of this invention consists simply of pouring test melts and heat treatment may be carried out at higher or lower temperatures with corresponding decrease or increase in time respectively. The term "artificial aging refers to the processing of the heat treated casting to precipitat out elements or compounds which have been put into solution during heat treatment. Artificial aging of the testing compositions was carried out by subjecting the heat treated casting to a temperature of 305 to 315 F. for three hours.

TABLE I Specimens produced by sand casting Alloying Elements 1 2 3 4 5 0 Magnesium 0 0. 50 0. 95 0 0. 0.75 Zlnc 5.5 5.5 5.5 5.5 5.5 5.5 Copper 3. 0 3.0 3.0 3.0 3.0 3.0 Silicon- 5. 5 5. 5 5. 5 5. 5 5. 5 5. 5 Iron 0. 46 0.46 0.46 0. 7O 0. 70 0. 70 Nickel 0. 04 0.04 0. 04 0.04 0.04 0. 04 ihriikatge Very Heavy Very Slight None Heavy Slight None s as Ultimate strength... 24, 200 29, 200 29, 200 23, 800 26, 500 30, 300

Elongation 2. 7 1. 7 1.2 l. 8 3. 0 l. 5 Heat Treatment:

Ultimate strength 32, 900 43, 500 28, 900 26, 500 60, 300

Elongation 4.0 2.0 1.9 3.0 l. 5

TABLE II Specimens produced by chill casting i gg s Medium Med. Slight Med. s1. Medium v. Slight None Ultimate Strength. 30,000 34, 600 34, 400 28, 500 35, 700 33, 200

Elongation 4. 5 1.8 l. 3 2. 8 1.9 1. 3 Heat Treated:

Ultimate Strength- 36,500 46, 800

Yield 16,400 34,900

Elongation 5. 7 2. 4

under equivalent conditions and observing the relative amounts of shrinkage produced in critical areas. The results secured are hereinafter defined as very heavy, heavy, slight, or no shrinkage.

In accordance with this invention, marked improvement in castability and other physical properties is secured by the addition of magnesium in amounts ranging from 0.2 to 1.0 percent by weight and preferably from 0.5 to 0.9 percent by weight to the elements of the base alloy. This improvement is especially significant in the manufacture of aluminum base casting alloys constituted with 2 to 4 percent copper, 2 to 8 percent zinc, 2 to 8 percent silicon, as major alloying elements. When the alloy is prepared of scrap materials, it is conceivable that it may b practically impossible to formulate entirely free of impurities, and in the practice of this invention, impurities such as iron and nickel have their effect. Yet, as much, if not more, than 0.2 percent nickel and 0.7 percent iron may be present.

Tables I and II are given to illustrate the improvements in physical properties secured by the addition of magnesium, as compared to corresponding aluminum base alloys prepared in the absence of such minor alloying elements, I?-

As shown in Tables I and H, shrinkage of the cast alloy is greatly reduced by the addition of magnesium to the base composition and such shrinkage is apparently completely eliminated when magnesium is present in the order of 0.75 and 0.95 percent by weight, notwithstanding the variation of impurities within limits. Important also is the noticeable increase in ultimate strength which follows from the addition of magnesium as an alloying element, such increased strengths being secured in the alloy in as cast condition or when subjected to solution heat treatment.

The addition of magnesium does not advantageously effect grain size, and in fact, at higher concentrations, the grain size seemingly is increased. When desired, small additions of titanium, within the range of 0.05 to 0.2 percent by weight, may be made without harmfully affecting the strength characteristics but noticeably 7o reducing the grain size to or below that existin TABLE 111 Physical properties as enacted by the addition of magnesium and titanium -I'N' SAND CASTING As a further concept of this invention, I have found that castability and other physical properties of the aluminum base alloy may be further improved by the addition of other minor alloying elements in combination with magnesium, with or without titanium. For purposes of clarity, the system may now be considered as constituting an aluminum base alloy having zinc, silicon, copper, and magnesium preferably in the proportions heretofore described.

In this system, the addition of chromium in amounts ranging from 0.05 to 1.0 percent by Weight and preferably from 0.10 to 0.45 percent completely overcome by the addition of titanium in the amounts previously described.

Chromium may be wholly or partially replaced by manganese in proportionately greater amounts ranging up to 1.5 percent, and best results are secured when the manganese content is maintained within the range of 0.15 to 0.8 percent by weight. The efiect of alloying the aluminum, zinc, copper, silicon and magnesium system with o chromium and manganese with or without titanium may be seen from Tables IV and V which compares the physical properties of an alloy constituted with about 5.5 percent by weight copper, 3.0 percent by weight zinc, 5.5 percent by weight by weight, has the effect of still further improvsilicon, 0.5 percent by Weight magnesium, the

ing the castability and the physical properties of the resulting alloy. Chromium has a tendency to coarsen the grain size, but this effect can be remainder being aluminum plus impurities, including 0.04 percent by weight nickel and 0.46 by weight iron.

TABLE IV Physical properties developed by sand casting Alloying Element 1 2 3 4 5 6 Magnesium 0 0 0. 50 0.50 0 50 0. 50 Chr0mium.- 0 2 0. 45 0. 25 Manganese. 0 15 0 15 0 0.15 0.15 0. 15 Titanium. 0.10 0. 10 Shrinkage. Very Slight None None None Medium Very Slight Grain Size 1. 25 1. 25 1. 43 1.00 0. 59 0. 83 As Cast:

Ultimate Strength. 29, 200 29, 300 31, 000 31, 500 27, 900 29, 600

Elongation 1. 7 1. 4 l. 5 1. 6 1. 1 1. 5 Heat Treated:

Ultimate Strength 43, 500 41, 600 41, 600 41, 300 31, 200

Elongation 2. 0 1. 9 1. 9 1. 1 1.8 Heat Treated and Aged:

Ultimate Strength. 43,100 42, 700 44, 400 45, 400 41, 900 42, 500

Elongation 1. 4 1. 9 1. 3 1. 0 1. 0 1. 9

TABLE V Physical properties developed by chill casting Alloying Elements 1 2 3 4 5 6 Magnesium 0. 50 0 50 0. 50 0. 50 0 50 0. 50 Chromium 0 25 0.45 0. 25 Manganese. 0. 0. 15 Titanium 0. 10 Shrinkage Very Slight Grain Size 0. 48 As Cast:

Ultimate Strength. 34, 600 35, 400 37, 37, 300 35, 400 36, 100

Elongation 1 2. 2 2. l 1. 9 2. 1 Heat Treated:

Ultimate Strength. 46, 800 50, 500 49, 900 47, 800 47, 900

Elongation. 2. 4 3. 9 4.1. 2. 3 3. 0 Heat Treated and Aged:

' Ultimate Strength- 45, 300 48, 800 52, 800 52, 300 45, 600 49, 800 Elongation 2 4 2.7 a 2. 2 3. 4

It will be noted from these tables that the greatest benefit from the described modifications with manganese and chromium resides in the increased values in ultimate strength and elongation. This is particularly evident in chill cast alloys which have been subjected to heat treat ment and to alloys which have been subjected to heat treatment followed by artificial ageing.

I have discovered further that certain physical properties and improved castability may be secured by the further addition with magnesium, chromium or manganese, with or without titanium, of a small amount of zirconium. Beneficial results are secured when zirconium is used in amounts ranging from 0.05 to 0.3 percent by weight, while best results are secured when zirconium in combination with chromium is added to the aluminum, zinc, silicon, copper, and magnesium system in an amount ranging from 0.10 to 0.25 percent.

Unlike chromium, zirconium affords some grain refining effect in either sand or chill casting, whether or not chromium or titanium are present. Unlike titanium, however, zirconium is not detrimental to casting properties when chromium or manganese is also present. In chill or permanent mold casting, zirconium further improves castability with or without chromium, manganese, and titanium.

Tables VI and VII illustrate the improvement in characteristics secured from tests of aluminum base alloys containing about 5.5 percent by weight silicon, 5.5 percent by weight copper, 3.0 percent by weight zinc, and impurities of the type including 0.46 percent iron and 0.04 percent nickel.

cast and sand cast alloys which have been subjected to heat treatment and in those alloys which have been subjected to heat treatment followed by artificial ageing. By the use of zirconium in combination with chromium and manganese,

- strength characteristics are secured which exceed values not heretofore contemplated for this type of alloy.

It will be apparent from the description that I have produced a new and improved alloy containing zinc, copper, and silicon as major alloying elements wherein improvements are secured by the addition of magnesium and by the addition of magnesium in combination with one or more other elements including chromium, manganese, zirconium and titanium. The improved results are secured when the alloy is processed by sand or chill casting and when the cast alloy is further heat treated with possible further processing by artificial ageing at relatively low temperatures.

It will be understood that numerous changes may be made in the ratio of materials one with another within the limitations prescribed and in the processing steps without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. An aluminum base casting alloy consisting essentially of 2-4 percent copper, 2-8 percent zinc, 2-8 percent silicon, 0.2-1.0 percent magnesium, 0.05-0.3 percent zirconium, a metal selected from the group consisting of 0.10-0.5 percent chromium and 0.15-0.8 percent manganese and mixtures thereof, the balance being aluminum.

TABLE VI Physical properties developed by sand casting Alloying Elements 1 2 3 4 5 6 7 Magnesium 0 0. 50 0. 50 0 50 0 50 0. 50 Chromium... 0.25 0.25 0. 25 Manganese. 0 15 0. l5 0. 15 0. 15 0. l5 0. 15 Titanium- 0. 10 0. 10 0. 10 Zinc 0.19 0. l) 0.19 0. l9 Shrinkage. Very Slight. Med. Slight.. None None Medium Heavy None Grain Size 1. 25 1. 25 1 25 0. 77 59 0.42 0.38 As Cast:

Ultimate Strength 29, 200 29, 800 29, 300 31, 100 27, 900 27, 700 30, 900 Elongation 1.7 1. 8 1. 1. 1. l 1. 4 1. 5 Heat Treated:

Ultimate Strength. 43, 500 39, 300 41, 600 42, 1'10 41, 300 38, 900 42, 300 Elongation 2.0 1.0 1.9 2. l 1.1 2. 0 Heat Treated and Aged:

Ultimate Strength.. 43, 100 42, 400 42, 700 44, 300 41, 900 39, 000 46, 000 Elongation l. 4 0.9 1. 0 1. 1.0 0.8 1.5

TABLE VII Physzcal propertzes developed by Chill castmg Alloying Elements 1 2 3 4 5 6 7 Magnesium 0. 50 0. 50 0.50 0. E0 0. 50 0 50 0.50 Chromium. 0.25 0. 25 0. 25 0.15 0.15 0. 15 0. 15 0. 15 0. 15 0. 10 0. 10 O. 10 0.19 0.19 0.19 0.19 Med. Slight V Slight None None Medium Medium V Slight Grain Size' 0. 40 0.35 0.50 0. 0.26 0.33 0.32 As Cast:

Ultimate Strength.... 34, 600 34, 200 35, 400 35, 800 35, 400 35, 300 35, 100 Elongation 1. 8 1. 8 2. 2 2. 4 1. 9 l. 8 2.0 Heat Treated:

Ultimate Strength.-.. 46, 800 46, 900 50, 500 51, 400 47, 800 45, 700 49, 000 Elongation 2. 4 2. 2 3. 9 4. 0 2. 3 2. 7 3. 9 Heat Treated and Aged:

Ultimate Strength--.. 45, 300 47, 500 48, 800 51,600 45,600 46, 500 50, 800 Elongation 2. 4 1. 2 3. 4 3. 1 2. 2 2. 2 1.8

The addition of zirconium is effective in practically every instance in improving the ultimate strength oi the alloy, as compared to an alloy composition in the absence of zirconium. Such 2. An aluminum base alloy consisting essentially of 2-4 percent by weight copper, 2-8 percent by weight zinc, 2-8 percent by weight silicon, 0.2-1.0 percent by weight magnesium, 0.05-

improvements are particularly evident in chill 0.3 percent by weight zirconium, 0.05-0.2 percent by weight titanium and a metal selected from the group consisting of 0.10-05 percent by Weight chromium and 0.15-1.5 percent by weight manganese and mixtures thereof as minor alloying elements, the remainder being aluminum.

3. An aluminum base alloy consisting essentially of 2-4 percent by weight copper, 2-8 percent by weight zinc, 2-8 percent by Weight silicon, 0.2-1.0 percent by weight magnesium, 0.05- 0.3 percent by weight zirconium, 0.05-02 percent by weight titanium and a metal selected from the group consisting of 0.05-11) percent by weight chromium, 0.15-1.5 percent by weight manganese and mixtures thereof as minor alloying elements, the remainder being aluminum.

4. An aluminum base alloy consisting essentially of 2-4 percent by weight copper, 2-8 percent by weight zinc, 2-8 percent by weight silicon, 0.2-1.0 percent by weight magnesium, 0.05-0.3 percent by weight zirconium and a metal selected from the group consisting of 005-10 percent by weight chromium and 0.15-1.5 percent by REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,572,489 Johnston et a1 Feb. 9, 1926 1,924,727 Rowe Aug. 29, 1933 2,098,081 Bates Nov. 2, 1937 2,240,940 Nock, Jr May 6, 1941 2,245,167 Stroup June 10, 1941 2,280,170 Stroup Apr. 21, 1942 2,290,016 Bonsack July 14, 1942 OTHER REFERENCES Ser. No. 337,047 (abandoned), Gauthier (A. P. (3.), published May 11, 1943. 

1. AN ALUMINUM BASE CASTING ALLOY CONSISTING ESSENTIALLY OF 2-4 PERCENT COPPER, 2-8 PERCENT ZINC, 2-8 PERCENT SILICON, 0.2-1.0 PERCENT MAGNESIUM, 0.05-0.3 PERCENT ZIRCONIUM, A METAL SELECTED FROM THE GROUP CONSISTING OF 0.10-0.5 PERCENT CHROMIUM AND 0.15-0.8 PERCENT MANGANESE AND MIXTURES THEREOF, THE BALANCE BEING ALUMINUM. 